The drying mechanism of high-value particles of hydroxyapatite in an industrial spray dryer was investigated numerically using the developed models and compared with the drying mechanism of silica droplets of the same final size. Similar mechanisms were observed for the drying of slurry droplets of both materials, but the rate of heat and mass transfer between air and droplets was lower, and the heat transfer resistance and heat accumulation in the dry crust was larger in the case of drying of hydroxyapatite droplets. The hydroxyapatite droplets were dried in a longer axial distance in the dryer, and the air temperature decreased and humidity increased more slowly during drying of hydroxyapatite droplets than in the case of silica. The temperature difference between the outer droplet surface and evaporation interface was significantly larger in the hydroxyapatite droplets than that in the silica due to the difference in thermal properties of solid materials. Less water vapour was accumulated in the dry crust of hydroxyapatite than in the crust layer of silica of the same thickness.
